The purpose of this project is to continue investigation, carried on since 1950, concerning Echinococcus species (Cestoda: Taeniidae) and the diseases caused by them in man (hydatid disease sensu lato). Principal objectives would be to distinguish the larval stages of four species of Echinococcus as they occur in human organs by means of morphologic characters not previously so applied; to evaluate the biological differences between the two "strains" of E. granulosus; to investigate cytogenetic methods as a further means for distinguishing species of Echinococcus; to assess the effect of mebendazole on the larval stage of E. multilocularis and of E. vogeli in situ in experimental animals infected per os; and to describe the post-embryonic development of E. vogeli in the intermediate host and define its pattern of growth and mechanism of pathogenesis. Investigations would be undertaken primarily in the laboratory, making extensive use of experimental animals (rodents) under controlled conditions but would be supplemented by field-studies as appropriate. Collaboration would continue with personnel at the Alaska Native Medical Center, U.S. Public Health Service, Anchorage, Alaska, and at the International Center for Medical Research, Cali, Columbia, making available materials from human and non-human subjects as well as clinical data and other information.